New: Callback for when the current page is set

This callback is executed later than onPageLoad, and is handy for triggering things that should happen when the document is fully in the viewer (onPageLoad gets triggered when the page is loaded, which may be outside of the viewport).
New: Callback for onDocumentLoaded

This callback is executed when the document has been loaded and is ready to go.
updated .gitignore
Update build directory
Merge branch 'master' of github.com:DDMAL/diva.js

Conflicts:
	build/js/diva.min.js